1. Field of the Invention
The present invention relates to a camera body, an accessory mounted between a camera body and an interchangeable lens, and a camera system including a camera body and an accessory.
2. Description of the Related Art
Conventionally, in a camera system configured so that communication between a camera body and an interchangeable lens is possible, optical specific information about the interchangeable lens is stored as an electronic data in the interchangeable lens. This optical specific information may be, for example, data indicating a relationship between a lens movement amount and a focus movement amount, data relating to a focus correction amount, focal length data, and aperture data. By transmitting such specific information to the camera at a suitable timing, autofocus (AF), autoexposure (AE) and the like are performed.
Further, an accessory is sometimes mounted between the camera body and the interchangeable lens. In such a case, the optical specific information about the interchangeable lens and the accessory put together is different from the optical specific information about the interchangeable lens alone. Consequently, a camera body or an interchangeable lens detects an accessory connection and corrects the above optical specific information.
However, when a camera body and an interchangeable lens with an old design and an accessory with a new design are used in combination, there is the problem that correction of such optical specific information cannot be performed. Here, the expression “new design” and “old design” is used with the following meaning. Specifically, “new design” refers to a newly designed accessory (new-design accessory) that cannot be detected by a conventional camera body or interchangeable lens (old-design camera body and interchangeable lens), or that does not have a correction value.
To resolve this problem, Japanese Patent Application Laid-Open No. 63-199336 discusses a system having a central processing unit (CPU) in an accessory, in which optical specific information relating to an accessory is rewritten by converting only the necessary communication between a camera and an interchangeable lens during communication. Further, Japanese Patent Application Laid-Open No. 2002-341424 discusses, when a camera body and an interchangeable lens system are older than an accessory, correcting optical specific information about the interchangeable lens in the accessory and transmitting the corrected information to the camera.
Due to manufacturing dispersion or errors of each individual camera, lens, and accessory, the optical specific information sometimes needs to be changed. In such a case, the correction data in the accessory needs to be rewritten based on the old/new restrictions in a system as described above. Further, to ensure the flexibility of the system, it is desirable that the data and the firmware in the accessory can be updated even after the accessory is in a user's possession. In addition, to perform such an update without a special input terminal or an additional part, it is necessary to operate the accessory via an existing camera mount.
Accessories are usually operated only after the camera body and the interchangeable lens have been combined. Therefore, to prevent mistaken operation, it is desirable that power flows to the accessory only after the above three units have been mounted together. More specifically, the accessory has amount unit for connecting the interchangeable lens. This mount unit has a switch that is physically turned ON as a result of the interchangeable lens being attached thereto. Further, as discussed in Japanese Patent Application Laid-Open Nos. 63-199336 and 2002-341424, when converting only the necessary communications in the accessory, other communications are directly transmitted from the camera to the lens. For example, if a dedicated command for rewriting the information in the accessory is newly provided, and transmitted from the camera side, the lens will also receive that command. If the lens side does not know that command, a malfunction can occur. Further, when rewriting the information in the accessory during the production process or a service deposit in each place, the interchangeable lens must always be provided on-site. It is a big disadvantage from the viewpoint of manufacturing cost and management cost to prepare the interchangeable lens for only feeding the accessory.
Therefore, instead of an interchangeable lens, a pseudo interchangeable lens could be used to turn the above switch ON. However, if a camera body, an accessory, and a pseudo interchangeable lens are combined, the camera body may not detect an interchangeable lens, so that communication per se may not even start. Further, even if a communication is sent, since a real interchangeable lens is not attached, normal communication is not performed. Normally, in such a case, the accessory either turns itself off to prevent unnecessary power consumption or enters a power saving state. This is because the battery is substantially consumed if an accessory with a pseudo interchangeable lens mounted is left attached to the camera. However, as described above, if the user wants to operate the accessory from the camera side, the accessory is in an inoperable state.